Radial vane air motors, or pneumatic motors, are widely used in industry particularly in portable tools. The design of such motors has evolved over the years to an optimum geometry for both "forward only" and "reversible" types. The design of the reversible motors, however, provides limited horsepower in forward operation as compared with a "forward only" motor. For example, one type of reversible motor is a mirror image type that is capable of producing in a forward rotation only seventy to eighty-five percent as much horsepower as a "forward only" type motor with the same displacement.
Conventional reversible radial vane air motors have ports and passages that conduct all or a part of the exhaust air through a reversing valve located on the end plate of the motor or in a backhead adjacent to the motor. Incorporating a governor into reversible motors makes these passages more complex, and the forward horsepower is reduced even further by backpressure through the reversing valve and the ports and passages.
Horsepower in the forward direction of a reversible motor is often enhanced by non-symmetric placement of ports. This results in a reduction of horsepower in the reverse direction. Another means for increasing horsepower in the forward direction is to include complex and elaborate slides and valves, but these complex motors have proven impractical in portable air tools. Thus, a need existed for a reversible radial vane governed air motor that can be easily incorporated into a portable pneumatic tool and achieve near full horsepower in the forward direction.